In Vivo Optical Interrogation of Neuronal Responses to Genetic, Cell Type-Specific Silencing

We established a low background, Cre-dependent version of the inducible Tet-On system for fast, cell type-specific transgene expression in vivo Coexpression of a constitutive, Cre-dependent fluorescent marker selectively allowed single-cell analyses before and after inducible, Tet-dependent transgene expression. Here, we used this method for precise, acute manipulation of neuronal activity in the living brain. The goal was to study neuronal network homeostasis at cellular resolution. Single induction of the potassium channel Kir2.1 produced cell type-specific silencing within hours that lasted for at least 3 d. Longitudinal in vivo imaging of spontaneous calcium transients and neuronal morphology demonstrated that prolonged silencing did not alter spine densities or synaptic input strength. Furthermore, selective induction of Kir2.1 in parvalbumin interneurons increased the activity of surrounding neurons in a distance-dependent manner. This high-resolution, inducible interference and interval imaging of individual cells (high I5, HighFive) method thus allows visualizing temporally precise, genetic perturbations of defined cells.SIGNIFICANCE STATEMENT Gene function is studied by KO or overexpression of a specific gene followed by analyses of phenotypic changes. However, being able to predict and analyze exactly those cells in which genetic manipulation will occur is not possible. We combined two prominent transgene overexpression methods to fluorescently highlight the targeted cells appropriately before cell type-specific transgene induction. By inducing a potassium channel that decreases neuronal firing, we investigated how neuronal networks in the living mouse brain possibly compensate swift changes in cellular activities. Unlike in vitro, known compensatory homeostatic mechanisms, such as changes in synapses, were not observed in vivo Overall, we demonstrated with our method rapid genetic manipulation and analysis of neuronal activities as well as precision transgene expression.

Generating Rab6 Conditional Knockout Mice

RAB6 GTPase is the most abundant Golgi-associated RAB protein and regulates several transport steps at the level of this organelle. Homozygous Rab6a knockout (k/o) is embryonic lethal in mouse. To study RAB6 function in cell lineages and tissues, we thus generated various conditional Rab6a knockout (k/o) mice using the Cre/lox system.

A food-grade expression system for d-psicose 3-epimerase production in Bacillus subtilis using an alanine racemase-encoding selection marker

Background

Food-grade expression systems require that the resultant strains should only contain materials from food-safe microorganisms, and no antibiotic resistance marker can be utilized. To develop a food-grade expression system for d-psicose 3-epimerase production, we use an alanine racemase-encoding gene as selection marker in Bacillus subtilis.

Results

In this study, the d-alanine racemase-encoding gene dal was deleted from the chromosome of B. subtilis 1A751 using Cre/lox system to generate the food-grade host. Subsequently, the plasmid-coded selection marker dal was complemented in the food-grade host, and RDPE was thus successfully expressed in dal deletion strain without addition of d-alanine. The selection appeared highly stringent, and the plasmid was stably maintained during culturing. The highest RDPE activity in medium reached 46 U/ml at 72 h which was comparable to RDPE production in kanamycin-based system. Finally, the capacity of the food-grade B. subtilis 1A751D2R was evaluated in a 7.5 l fermentor with a fed-batch fermentation.

Conclusion

The alanine racemase-encoding gene can be used as a selection marker, and the food-grade expression system was suitable for heterologous proteins production in B. subtilis.

Electronic supplementary material

The online version of this article (doi:10.1186/s40643-017-0139-7) contains supplementary material, which is available to authorized users.

Cre-inducible site-specific recombination in zebrafish oligodendrocytes

BACKGROUND

The conditional Cre/lox system has recently emerged as a valuable tool for studies on both embryonic and adult Zebrafish. Temporal control and site-specific recombination are achieved by using the ligand-inducible CreER^T2 and administration of the drug tamoxifen (TAM) or its active metabolite, 4-Hydroxytamoxifen (4-OHT).

RESULTS

Here we report the generation of a transgenic Zebrafish line, which expresses an mCherry-tagged variant of CreER^T2 under the control of the myelin basic protein a (mbpa) promoter. Our analysis shows that larval and adult expression of the transgene recapitulates the endogenous mbpa expression pattern in oligodendrocytes. Furthermore, combination with a Cre-dependent EGFP reporter results in EGFP-expressing oligodendrocytes in the spinal cord, brain, and optic nerve in TAM- or 4-OHT-treated larvae and 4-month-old fish, but not in untreated controls.

CONCLUSIONS

The transgenic Zebrafish line Tg(mbpa:mCherry-T2A-CreER^T2 ) elicits CreER^T2 expression specifically in myelinating glia cells. Cre-inducible targeted recombination of genes in oligodendrocytes will be useful to elucidate cellular and molecular mechanisms of myelination in vivo during development (myelination) and regeneration (remyelination) after injury to the central nervous system (CNS). It will also allow targeted expression and overexpression of genes of interest (transgenes) in oligodendrocytes at defined developmental and adult stages. Developmental Dynamics 246:41-49, 2017. © 2016 Wiley Periodicals, Inc.